ProSoundWeb Community

Please login or register.

Login with username, password and session length
Advanced search  

Pages: 1 ... 3 4 [5] 6 7 ... 10   Go Down

Author Topic: Combiner quality  (Read 28029 times)

Jason Glass

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 918
    • CleanWirelessAudio.com
Re: Combiner quality
« Reply #40 on: April 19, 2018, 03:31:21 PM »

I get that, but are there actual numbers? I suspect nobody has done any head to heads between these devices in a controlled setting so it’s very difficult to quantify the real world differences I expect.
Wish I had the time and RF chops to do it!


Sent from my iPhone using Tapatalk Pro

Jason Glass

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 918
    • CleanWirelessAudio.com
Re: Combiner quality
« Reply #41 on: April 19, 2018, 03:32:07 PM »

I get that, but are there actual numbers? I suspect nobody has done any head to heads between these devices in a controlled setting so it’s very difficult to quantify the real world differences I expect.
Wish I had the time and RF chops to do it!


Sent from my iPhone using Tapatalk Pro

Jason Glass

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 918
    • CleanWirelessAudio.com
Re: Combiner quality
« Reply #42 on: April 19, 2018, 03:33:02 PM »

I get that, but are there actual numbers? I suspect nobody has done any head to heads between these devices in a controlled setting so it’s very difficult to quantify the real world differences I expect.
Wish I had the time and RF chops to do it!


Sent from my iPhone using Tapatalk Pro

This TX-8 was a prototype.  Production units are much quieter.
« Last Edit: April 19, 2018, 03:36:20 PM by Jason Glass »
Logged

Jason Glass

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 918
    • CleanWirelessAudio.com
Re: Combiner quality
« Reply #43 on: April 19, 2018, 03:33:47 PM »

I get that, but are there actual numbers? I suspect nobody has done any head to heads between these devices in a controlled setting so it’s very difficult to quantify the real world differences I expect.
Wish I had the time and RF chops to do it!


Sent from my iPhone using Tapatalk Pro

Andrew Broughton

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 2315
    • Check Check One Two
Re: Combiner quality
« Reply #44 on: April 19, 2018, 06:39:37 PM »

Thank you so much, Jason!

I can't be reading these right, as it seems like the AC-3 has the best trace with the lowest IM!
Logged
-Andy

"Well, my days of not taking you seriously are certainly coming to a middle..."

http://www.checkcheckonetwo.com
Saving lives through Digital Audio, Programming and Electronics.

Mac Kerr

  • Old enough to know better
  • Administrator
  • Hero Member
  • *****
  • Offline Offline
  • Posts: 7552
  • Audio Plumber
Re: Combiner quality
« Reply #45 on: April 19, 2018, 07:19:51 PM »

Thank you so much, Jason!

I can't be reading these right, as it seems like the AC-3 has the best trace with the lowest IM!

The AC-3 seems to have the lowest noise floor, but it also has the lowest output level. All the other units appear to be about 10dB hotter on the output. They all look pretty good as far as IM products. The prototype TX8 and older GX8 both seem to suffer from noise or low level IM products, but they are both capable of a lot of gain.

Mac
Logged

Scott Holtzman

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 7536
  • Ghost AV - Avon Lake, OH
    • Ghost Audio Visual Systems, LLC
Re: Combiner quality
« Reply #46 on: April 19, 2018, 07:33:48 PM »

Thank you so much, Jason!

I can't be reading these right, as it seems like the AC-3 has the best trace with the lowest IM!

I count 14 birdies above the reference line on the AC-3

One thing to add that hasn't been brought up.  A combiner should also have a circulator on the output (think of it as an RF diode).  Backfeeding down the output contributes to more IM products.

A general comment about the 100mw power level.  You can make a lot of heat with 100mw.  Back in the day before digital cellular one of the largest design challenges was the duplexor (combines the RX and TX into a single antenna) even with the almost 50Mhz of spread the filter still had some loss which is dissipated as heat.  Carrying that heat away from a PC board mounted stripline type device was a bitch.  Most people thought the final amplifier was generating the heat but the hottest device in the radio was the combiner and circulator.

Logged
Scott AKA "Skyking" Holtzman

Ghost Audio Visual Solutions, LLC
Cleveland OH
www.ghostav.rocks

Andrew Broughton

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 2315
    • Check Check One Two
Re: Combiner quality
« Reply #47 on: April 19, 2018, 07:53:56 PM »

The AC-3 seems to have the lowest noise floor, but it also has the lowest output level. All the other units appear to be about 10dB hotter on the output. They all look pretty good as far as IM products. The prototype TX8 and older GX8 both seem to suffer from noise or low level IM products, but they are both capable of a lot of gain.

Mac
I wonder if the AC3 and Combine-4 would have the same performance?

I'm still having trouble deciding if the MUCH higher price of the 8ch combiners is justified in my case. I understand that if you need it you need it, regardless of cost. I'm just not sure if I need it! My biggest headache these days is LED video walls. I'm not sure if a combiner can help me with that!
Logged
-Andy

"Well, my days of not taking you seriously are certainly coming to a middle..."

http://www.checkcheckonetwo.com
Saving lives through Digital Audio, Programming and Electronics.

Jason Glass

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 918
    • CleanWirelessAudio.com
Re: Combiner quality
« Reply #48 on: April 20, 2018, 05:51:33 PM »

I wonder if the AC3 and Combine-4 would have the same performance?

I'm still having trouble deciding if the MUCH higher price of the 8ch combiners is justified in my case. I understand that if you need it you need it, regardless of cost. I'm just not sure if I need it! My biggest headache these days is LED video walls. I'm not sure if a combiner can help me with that!
Hi Andrew,

Your observation is accurate; the AC-3 is very quiet when combining 30mW signals, below its spec'd limit. The others are transmitting 100mW.  I also failed to note that the others are combining 8 channels, which aren't visible because they're outside of the SA span shown.

When your trouble is because of wideband interference sources local to RX, such as video walls stomping IEM packs, you have roughly seven choices:
1. Attenuate RX antenna input.
2. Increase TX power.
3. Identify specific freqs where noise generated by local sources is lowest at the RX antennas and tune your IEMs to those.
4. Insert external narrow bandpass filters on RX.
5. All or most of the above.
6. Identify and shield specific components that are radiating interfering noise.
7. Change IEM systems' tuning bandwidth to one outside of local interference noise band.

FWIW, 4 is damned near impossible for IEM within practical physical size, performance specs, and budget limits. 6 is also difficult because linked LED arrays often act as a single, large area source of low level RF energy. 2 is where the best combiner that you can afford is critical, because it makes both 2 and 3 possible without generating excessive IMD on freqs that you're stuck with, regardless of IMD prediction math.

Sent from my Nexus 5 using Tapatalk

Andrew Broughton

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 2315
    • Check Check One Two
Re: Combiner quality
« Reply #49 on: April 20, 2018, 07:13:55 PM »

Hi Andrew,

Your observation is accurate; the AC-3 is very quiet when combining 30mW signals, below its spec'd limit. The others are transmitting 100mW.  I also failed to note that the others are combining 8 channels, which aren't visible because they're outside of the SA span shown.

When your trouble is because of wideband interference sources local to RX, such as video walls stomping IEM packs, you have roughly seven choices:
1. Attenuate RX antenna input.
2. Increase TX power.
3. Identify specific freqs where noise generated by local sources is lowest at the RX antennas and tune your IEMs to those.
4. Insert external narrow bandpass filters on RX.
5. All or most of the above.
6. Identify and shield specific components that are radiating interfering noise.
7. Change IEM systems' tuning bandwidth to one outside of local interference noise band.

FWIW, 4 is damned near impossible for IEM within practical physical size, performance specs, and budget limits. 6 is also difficult because linked LED arrays often act as a single, large area source of low level RF energy. 2 is where the best combiner that you can afford is critical, because it makes both 2 and 3 possible without generating excessive IMD on freqs that you're stuck with, regardless of IMD prediction math.

Sent from my Nexus 5 using Tapatalk


Thank you once again, Jason. James also recommended using the RF pads on the PSM1000. (https://www.rfvenue.com/blog/2015/08/25/four-proven-strategies-for-fighting-video-wall-rf-interference)

As if it wasn't bad enough with all the frequency ranges being gobbled up by Telcoms, now we have Video Walls to deal with. RF world sure isn't getting any better.
Logged
-Andy

"Well, my days of not taking you seriously are certainly coming to a middle..."

http://www.checkcheckonetwo.com
Saving lives through Digital Audio, Programming and Electronics.

ProSoundWeb Community

Re: Combiner quality
« Reply #49 on: April 20, 2018, 07:13:55 PM »


Pages: 1 ... 3 4 [5] 6 7 ... 10   Go Up
 



Site Hosted By Ashdown Technologies, Inc.

Page created in 0.022 seconds with 25 queries.